Patients may be caught off guard if their doctor asks the last question during an annual checkup. Here’s why we inquire. The retina, or the back of the eye, is the only place in your body that gives doctors a close-up view of your blood vessels and nerves without your needing to be cut open. This makes a routine eye exam very useful for detecting important medical issues at their earliest stages. We at The Doctors asked some of our trusted eye-care experts to tell us which conditions they may help diagnose during your regular exam. And don't miss these secrets that eye doctors won't tell you.

Cancer

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An eye exam may save your life. We can find everything from brain tumors to breast and lung cancers that have spread to the eye, says Joseph Pizzimenti, an optometrist and associate professor at Nova Southeastern University College of Optometry Eye Care Institute in Fort Lauderdale, Florida. Certain types of bleeding in the retina can signal leukemia. Eye doctors can diagnose brain tumors based on changes in a patient’s field of vision. Malignant melanoma can strike in back of the eye, and patients often don’t know it is there unless the cancer is in the very center of their field of vision, Pizzimenti says. These are common cancer symptoms women are likely to ignore and these are cancer signs men can easily overlook.

Diabetes

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One of the first clues for type 2 diabetes may be a small amount of bleeding in the retina, which is a symptom of diabetic retinopathy. “I see patients every day who have this damage and who haven’t yet been diagnosed with diabetes,” says Pizzimenti. Left untreated, the condition can lead to blindness, but managing it cuts this risk in half. When diabetic retinopathy is detected early, lifestyle changes such as eating healthier and losing weight can help prevent further damage. It's easy for people to miss these silent symptoms of diabetes.

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High blood pressure

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Blood vessel damage, including weakening and narrowing of the arteries, can signal high blood pressure, says Jessica Ciralsky, MD, assistant professor of ophthalmology at Weill Cornell Medical College in New York City. Multiple large-scale studies have found links between heart disease and narrowing of small blood vessels in the retina, according to a paper in the American Journal of Medicine. These connections are particularly strong in people without traditional heart disease risk factors.

Multiple sclerosis

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Optic neuritis—inflammation of the optic nerve—can be a harbinger of MS, a degenerative disease of the nervous system, says Mitchell Munson, president of the American Optometric Association. Optic neuritis occurs in 75 percent of patients with MS and is the first symptom of the disease in up to 25 percent of cases. (A diagnosis of optic neuritis doesn’t automatically mean you have MS; it could also be the result of an infection or other causes.) “Patients with optic neuritis often have blurred vision, but I have diagnosed this in some people with no symptoms at all,” Munson says. These early symptoms of multiple sclerosis are often silent.

Rheumatoid arthritis

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About 25 percent of RA patients have eye issues; dry eye is the most common. Another clue: “If a patient has two bouts of iritis—painful inflammation of the iris, or the colored part—in a year, or three in 18 months, we suspect rheumatoid arthritis,” Munson says. People with RA, an inflammatory disease that affects small joints in the hands and feet, have high levels of inflammatory chemicals in their blood. Sometimes these can migrate to the eyeball as well as to the joints, explains Munson.